Showing papers by "Xiaohua Ma published in 2012"

High-performance Sn–Ni alloy nanorod electrodes prepared by electrodeposition for lithium ion rechargeable batteries

Abstract: To reduce irreversible capacity and improve cycle performance of tin used in lithium ion batteries, Sn–Ni alloy nanorod electrodes with different Sn/Ni ratios were prepared by an anodic aluminum oxide template-assisted electrodeposition method. The structural and electrochemical performance of the electrode were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, cyclic voltammetry, and galvanostatic charge–discharge cycling measurement. The results showed that the copper substrate is covered with uniformly distributed Sn–Ni alloy nanorods with an average diameter of 250 nm. Different phases (Sn, Ni3Sn4 and metastable phases) of alloy nanorod formed in the electrodeposition baths with different compositions of Sn2+ and Ni2+ ions. Sn–Ni alloy nanorod electrode delivered excellent capacity retention and rate performance.

Fabrication and characterization of InAlN/GaN-based double-channel high electron mobility transistors for electronic applications

Abstract: In our previous work [J S Xue et al, Appl Phys Lett 100, 013507 (2012)], superior electron-transport properties are obtained in InAlN/GaN/InAlN/GaN double-channel (DC) heterostructures grown by pulsed metal organic chemical vapor deposition (PMOCVD) In this paper, we present a detailed fabrication and systematic characterization of high electron mobility transistors (HEMTs) fabricated on these heterostructures The device exhibits distinct DC behavior concerning with both static-output and small-signal performance, demonstrating an improved maximum drain current density of 1059 mA/mm and an enhanced transconductance of 223 mS/mm Such enhancement of device performance is attributed to the achieved low Ohmic contact resistance as low as 033 ± 005 Ω·mm Moreover, very low gate diode reverse leakage current is observed due to the high quality of InAlN barrier layer deposited by PMOCVD A current gain frequency of 10 GHz and a maximum oscillation frequency 21 GHz are also observed, which are comparable to the state-of-the-art AlGaN/GaN-based DC HEMT found in the literature The results demonstrate the great potential of PMOCVD for application in InAlN-related device’s epitaxy

Neutron irradiation effects on AlGaN/GaN high electron mobility transistors

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) were exposed to 1 MeV neutron irradiation at a neutron fluence of 1 × 1015 cm−2. The dc characteristics of the devices, such as the drain saturation current and the maximum transconductance, decreased after neutron irradiation. The gate leakage currents increased obviously after neutron irradiation. However, the rf characteristics, such as the cut-off frequency and the maximum frequency, were hardly affected by neutron irradiation. The AlGaN/GaN heterojunctions have been employed for the better understanding of the degradation mechanism. It is shown in the Hall measurements and capacitance—voltage tests that the mobility and concentration of two-dimensional electron gas (2DEG) decreased after neutron irradiation. There was no evidence of the full-width at half-maximum of X-ray diffraction (XRD) rocking curve changing after irradiation, so the dislocation was not influenced by neutron irradiation. It is concluded that the point defects induced in AlGaN and GaN by neutron irradiation are the dominant mechanisms responsible for performance degradations of AlGaN/GaN HEMT devices.

Channel temperature determination of a multifinger AlGaN/GaN high electron mobility transistor using a micro-Raman technique

Abstract: Self-heating in a multifinger AlGaN/GaN high electron mobility transistor (HEMT) is investigated by micro-Raman spectroscopy. The device temperature is probed on the die as a function of applied bias. The operating temperature of the AlGaN/GaN HEMT is estimated from the calibration curve of a passively heated AlGaN/GaN structure. A linear increase of junction temperature is observed when direct current dissipated power is increased. When the power dissipation is 12.75 W at a drain voltage of 15 V, a peak temperature of 69.1 °C is observed at the gate edge on the drain side of the central finger. The position of the highest temperature corresponds to the high-field region at the gate edge.

The effects of proton irradiation on the electrical properties of NbAlO/AlGaN/GaN MIS-HEMT

Abstract: AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistors (MIS-HEMTs) with atomic layer deposited (ALD) NbAlO gate dielectric were investigated using 3 MeV proton irradiation at a fluence of 1015 p/cm2. It was found that the proton irradiation damage caused degradation in DC performance and a flatband voltage shift in the capacitance-voltage curve. Gate-drain conductance measurements indicated that new traps were introduced in GaN from the irradiation, and the trap densities increased from 1.18×1012 cm−2·eV−1 to 1.82×1012 cm−2·eV-1 in MIS-HEMTs after irradiation. However, these increases in trap densities caused by irradiation in MIS-HEMT are less than those in HEMT, which can be attributed to the protection of the AlGaN surface by the NbAlO dielectric layer.

InGaN solar cell with p-i-n sandwich structure

Abstract: The invention discloses an InGaN solar cell with a p-i-n sandwich structure, mainly solving the problem of low conversion efficiency of the traditional InGaN solar cell. The solar cell comprises a substrate, an AlN nucleating layer (11) growing at high temperature, an unintentionally-doped GaN buffer layer (12), an n-GaN layer (13), an i-InGaN layer (14) and a p-GaN layer (15) in sequence from bottom to top, wherein the thickness of the n-GaN layer (13) is 50-100nm, and the electron concentration of the n-GaN layer (13) is 1*10 -6*10 /cm ; the thickness of the i-InGaN layer (14) is 100-800nm, the carrier concentration of the i-InGaN layer (14) is 1*10 -2*10 /cm , and the In component of the i-InGaN layer (14) is 15-90 percent; the thickness of the p-GaN layer (15) is 50-100nm and the hole concentration of the p-GaN layer (15) is 1*10 -6*10 /cm ; and grid Ni/Au ohmic electrodes (16) are distributed on the surface of the p-GaN layer (15), and an Al/Au ohmic electrode (17) is extracted from the right side of the surface of the n-GaN layer (15). According to the InGaN solar cell with the p-i-n sandwich structure, the short-circuited current and the open-circuited voltage of the cell are increased, and higher conversion efficiency is achieved; and the InGaN solar cell with the p-i-n sandwich structure can be used for solar photovoltaic power generation.

Metal insulated semi-conductor (MIS) grid GaN base enhancing high electro mobility transistor (HEMT) device and manufacture method

Abstract: The invention discloses a metal insulated semi-conductor (MIS) grid GaN base enhancing high electro mobility transistor (HEMT) device and a manufacture method, which mainly solve the problems that the existing GaN base enhancing device is low in threshold voltage, poor in controllability and low in reliability. The device comprises a substrate (1), a transition layer (2), a GaN main buffering layer (3) and an N-type AlGaN main barrier layer (4). A source (9) and a drain (10) are arranged on two sides of the top end of the N-type AlGaN main barrier layer (4), a grid (13) is arranged in the middle of the top end of the source (9) and the drain (10), a groove (5) is etched in the middle of the GaN main buffering layer (3), the bottom of the groove is a 0001 polarity plane, a lateral side of the groove is a non-0001 plane, and an inner wall of the groove extends outwards to form a GaN auxiliary buffering layer (6), a AlGaN auxiliary barrier layer (7) and a medium layer (8). The grid (13) is deposited on the medium layer (8). The MIS grid GaN base enhancing HEMT device and the manufacture method have the advantages of being high in threshold voltage, good in regulation performance, high in current density, good in pinching-off performance, simple and mature in manufacture process and good in repeatability and can be used for high temperature high power application situations and digital circuits.

AlGaN/GaN Metal-Insulator-Semiconductor High Electron-Mobility Transistor Using a NbAlO/Al 2 O 3 Laminated Dielectric by Atomic Layer Deposition

Abstract: We investigate the characteristics of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a NbAlO/Al2O3 lamination dielectric deposited by atomic layer deposition (ALD) as the gate insulator. A large gate voltage swing (GVS) of 3.96 V and a high breakdown voltage of −150 V for the MIS-HEMT were obtained. We present the gate leakage current mechanisms and analyze the reason for the reduction of the leakage current. Compared with traditional HEMTs, the maximum drain current is improved to 960 mA/mm, indicating that NbAlO layers could reduce the surface-related depletion of the channel layer and increase the sheet carrier concentration. In addition, the maximum oscillation frequency of 38.8 GHz shows that the NbAlO high-k dielectric can be considered as a potential gate oxide comparable with other dielectric insulators.